Spend 1000gp to make MW Rapier magical.
Purchase +1 Light Crossbow - 1385gp
Levelling to 7 (Rogue 6): +1BAB, +1 to all saves, Trapfinding +2, Rogue Talent (Finesse Rogue - gains Weapon Finesse as a bonus feat)
Skill points (+10): +2 Acrobatics, +1 Diplomacy, +2 Disable Device, +1 Escape Artist, +2 Swim, +2 UMD.
Feat: Two Weapon Fighting.
Notes: There is an underwater light crossbow in the Ranged Tactics toolbox - https://www.aonprd.com/EquipmentWeaponsDisplay.aspx?ItemName=Underwater%20light%20crossbow - A +1 of those would be 1420gp. Maybe that's the Aventi style Rani was interested in.
Also - if possible, Rani would like to get the Rogue Trick of Hold Breath that's in Ultimate Combat [A rogue with this talent increases the number of rounds she can hold her breath by 2. She can take this talent multiple times.]